This invention relates to devices for measuring magnetic fields, and, more particularly, to a sensitive thin-film magnetometer that is planar yet can measure the three orthogonal components of a very small magnetic field.
A magnetometer is a device that measures the presence and magnitude of a magnetic field, and, in the case of a vector magnetometer, the direction of the magnetic field. In a conventional magnetometer, an input loop (or coil) of an electrical conductor is placed into a varying magnetic field. The magnetic flux passing through the loop creates a responsive movement of electrical charge. The resulting electrical current is measured, and the magnetic field is calculated from the measured electrical current.
It is usually important to understand both the direction and the magnitude of the magnetic field. A magnetic field can be visualized as a vector having orthogonal components along three axes. To characterize the magnetic field completely, the magnetometer may have either three separate loops oriented perpendicular to the axes of interest, or a single loop whose orientation can be changed until it is perpendicular to the magnetic field. In the case of the three-axis magnetometer the components of the magnetic field are individually measured and the total magnetic field can be calculated, and in the case of the single movable loop the total field is measured and the components can be calculated.
In some areas of technology it is desirable, but difficult, to measure the local character of a magnetic field with accuracy and very high spatial resolution. For example, where the magnetic field is emitted from a solid body it is desirable to measure the magnetic field at various locations adjacent the solid body in order to understand its origin. Such circumstances arise in biomagnetometry, the study of magnetic field arising from the human body, and in nondestructive testing, the study of the integrity of a body from external measurements that do not adversely influence the body.
To achieve a particular spatial resolution in such circumstances, the magnetometer loop or loops must be made with a lateral dimension on the same order of size as the desired spatial resolution. To achieve good accuracy, the magnetometer loop must be placed as closely as possible to the body whose magnetic field is to be measured. One inherent limiting factor in such measurements is that, as the loop is made smaller so that it can achieve good spatial resolution and be placed close to the surface, the current detector must be made more sensitive because the loop receives a lower magnetic flux per unit time than does a larger loop. Also, as the loop or loops are made smaller, it becomes progressively more difficult to controllably and reproducibly orient the loop or loops adjacent the body to be measured. The components of the magnetic field parallel to the surface of the body are particularly difficult to measure, because the loops must be oriented with their normal vectors parallel to the surface.
There is a continuing need for a magnetometer that achieves both high sensitivity and high spatial resolution for magnetic fields originating in a body. Such a magnetometer must be able to measure all three components of the magnetic field vector. The present invention fulfills this need, and further provides related advantages.